Certification of Turbojets, 41522-41556 [E9-19350]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 74, Number 157 (Monday, August 17, 2009)]
[Proposed Rules]
[Pages 41522-41556]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E9-19350]



[[Page 41521]]

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Part III





Department of Transportation





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Federal Aviation Administration



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14 CFR Parts 1 and 23



Certification of Turbojets; Proposed Rule

Federal Register / Vol. 74, No. 157 / Monday, August 17, 2009 / 
Proposed Rules

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 1 and 23

[Docket No. FAA-2009-0738; Notice No. 09-09]
RIN 2120-AJ22


Certification of Turbojets

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This action proposes to enhance safety by amending the 
applicable standards for part 23 turbojet-powered airplanes--which are 
commonly referred to as ``turbojets''--to reflect the current needs of 
industry, accommodate future trends, address emerging technologies, and 
provide for future airplane operations. This action is necessary to 
eliminate the current workload of processing exemptions, special 
conditions, and equivalent levels of safety findings necessary to 
certificate light part 23 turbojets. The intended effect of the 
proposed changes would: Standardize and simplify the certification of 
part 23 turbojets; clarify areas of frequent non-standardization and 
misinterpretation, particularly for electronic equipment and system 
certification; and codify existing certification requirements in 
special conditions for new turbojets that incorporate new technologies.

DATES: Send your comments on or before November 16, 2009.

ADDRESSES: You may send comments identified by Docket Number FAA-2009-
0738 using any of the following methods:
     Federal eRulemaking Portal: Go to https://www.regulations.gov and follow the online instructions for sending your 
comments electronically.
     Mail: Send comments to Docket Operations, M-30, U.S. 
Department of Transportation, 1200 New Jersey Avenue, SE., Room W12-
140, West Building Ground Floor, Washington, DC 20590-0001.
     Hand Delivery or Courier: Bring comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.

For more information on the rulemaking process, see the SUPPLEMENTARY 
INFORMATION section of this document.
    Privacy: We will post all comments we receive, without change, to 
https://www.regulations.gov, including any personal information you 
provide. Using the search function of our docket Web site, anyone can 
find and read the electronic form of all comments received into any of 
our dockets, including the name of the individual sending the comment 
(or signing the comment for an association, business, labor union, 
etc.). You may review DOT's complete Privacy Act Statement in the 
Federal Register published on April 11, 2000 (65 FR 19477-78) or you 
may visit https://DocketsInfo.dot.gov.
    Docket: To read background documents or comments received, go to 
https://www.regulations.gov at any time and follow the online 
instructions for accessing the docket. Or, go to Docket Operations in 
Room W12-140 of the West Building Ground Floor at 1200 New Jersey 
Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through 
Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: For technical questions concerning 
this proposed rule, contact Pat Mullen, Regulations and Policy, ACE-
111, Federal Aviation Administration, 901 Locust St., Kansas City, MO 
64106; telephone: (816) 329-4111; facsimile (816) 329-4090; e-mail: 
pat.mullen@faa.gov. For legal questions concerning this proposed rule, 
contact Mary Ellen Loftus, ACE-7, Federal Aviation Administration, 901 
Locust St., Kansas City, MO 64106; telephone: (816) 329-3764; e-mail: 
mary.ellen.loftus@faa.gov.

SUPPLEMENTARY INFORMATION: Later in this preamble under the Additional 
Information section, we discuss how you can comment on this proposal 
and how we will handle your comments. Included in this discussion is 
related information about the docket, privacy, and the handling of 
proprietary or confidential business information. We also discuss how 
you can get a copy of this proposal and related rulemaking documents.

Authority for This Rulemaking

    The FAA's authority to issue rules on aviation safety is found in 
Title 49 of the United States Code. Subtitle I, Section 106 describes 
the authority of the FAA Administrator. Subtitle VII, Aviation Programs 
describes in more detail the scope of the agency's authority.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701. Under that section, 
the FAA is charged with promoting safe flight of civil airplanes in air 
commerce by prescribing minimum standards required in the interest of 
safety for the design and performance of airplanes. This regulation is 
within the scope of that authority because it prescribes new safety 
standards for the design of normal, utility, acrobatic, and commuter 
category airplanes.

Table of Contents

I. Background
    A. Historical Certification Requirements Overview
    B. Aviation Rulemaking Committee (ARC) Recommendations
    C. Proposed Regulatory Requirements Overview
II. Discussion of the Proposed Regulatory Requirements
III. Regulatory Notices and Analyses
IV. The Proposed Amendments

I. Background

A. Historical Certification Requirements Overview

    Title 14 Code of Federal Regulations (14 CFR) part 23 provides the 
airworthiness standards for Normal, Utility, Acrobatic, and Commuter 
Category Airplanes. The first application for the certification of a 
turbojet airplane under part 23 occurred in the 1970s before many of 
the current turbine requirements were added to part 23. Prior to this, 
turbojet powered airplanes were certificated to the standards under 
part 25. Part 25 provides the airworthiness standards for Transport 
category airplanes. A turbojet is a jet engine that develops thrust 
using a turbine compressor which is propelled by high speed exhaust 
gases expelled as a jet. The FAA implemented many of the certification 
requirements for early part 23 turbojets through special conditions 
based on 14 CFR part 25 (pre-amendment 25-42, (43 FR 2320)) 
requirements. Almost all special conditions applied to turbojets were 
for part 23, subpart B, Flight, and subpart G, Operating Limitations 
and Information.
    Special conditions for part 23 certification increased performance 
requirements for emerging turbojets similar to those covered by early 
part 25 standards. The FAA established these special conditions to 
ensure a minimum one-engine inoperative (OEI) performance level that 
would be included in the airplane's limitations, thereby guaranteeing 
single-engine climb performance. The level of safety provided by the 
special conditions was purposely higher for the early turbojets than 
for propeller-driven airplanes in the same weight band because the 
manufacturers and the FAA wanted part 23 turbojets to be similar to 
part 25

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business jets. Special conditions also addressed the following safety 
concerns: (1) The lack of turbine requirements in part 23, (2) the 
sensitivity of turbine engines to altitude and temperature effects, and 
(3) the high takeoff and landing speeds associated with turbojets that 
typically required long takeoff and landing distances, as compared to 
the performance of reciprocating, multiengine airplanes of that era.
    In the mid-1990s, the FAA hosted a meeting for flight test pilot 
representatives from the Aircraft Certification Offices. The purpose of 
that meeting was to discuss how emerging 600 to 1,200 pound thrust 
engines were being developed and how the FAA would certificate future 
turbojet programs. The participants considered the prospect for small 
single- and multi-engine turbojets. At that time, the FAA assumed that 
any new part 23 turbojet would have similar characteristics to any 
existing small part 25 turbojet. However, using the preliminary design 
estimates from several new turbojets, FAA flight test personnel 
realized these assumptions were outdated. Therefore, the FAA needed to 
reevaluate its certification standards for turbojets against existing 
light-weight airplanes.
    The meeting participants did not want to discourage development of 
small part 23 turbojets by applying significantly higher standards than 
for an equivalent propeller airplane. Therefore, the participants 
decided the best approach for future turbojet certification programs 
was to apply the existing part 23 weight differentiator of 6,000 pounds 
in establishing requirements.

B. Aviation Rulemaking Committee (ARC) Recommendations

    On February 3, 2003, we published a notice announcing the creation 
of the part 125/135 Aviation Rulemaking Committee.\1\ Part 125 
addresses the certification and operations of airplanes having a 
seating capacity of 20 or more passengers or a maximum payload capacity 
of 6,000 pounds or more. Part 135 addresses the operating requirements 
for commuter and on-demand operations and rules governing persons on 
board such aircraft. Since some part 23 airplanes operate under parts 
125 or 135, the ARC provided recommendations to the FAA for safety 
standards applicable for part 23 turbojet airplanes to reflect the 
current industry, industry trends, emerging technologies and operations 
under parts 125 and 135, and associated regulations. The ARC also 
reviewed the existing part 23 certification requirements and the 
accident history of light piston-powered, multiengine airplanes up 
through small turbojets used privately and for business. In addition, 
the ARC reviewed the special conditions applied to part 23 turbojets. 
The ARC completed its work in 2005 and submitted its recommendations to 
the FAA. Those documents may be reviewed in the docket for this 
proposed rule. The ARC recommended modifying forty-one 14 CFR part 23 
sections as a result of its review of these areas.
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    \1\ 68 FR 5488
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    As stated earlier, the FAA's intent is to codify standards 
consistent with the level of safety currently required through special 
conditions. We compared the special conditions applied to part 23 
turbojets, as well as several additional proposed part 23 changes, with 
the ARC's recommendations. With few exceptions, the ARC recommendations 
validated the FAA's long-held approach to certification of part 23 
turbojets.
    The ARC did not want to impose commuter category takeoff speeds for 
turbojets above 6,000 pounds, nor did the ARC want to impose more 
stringent requirements for one-engine inoperative (OEI) climb 
performance than those established for similar-sized piston-powered and 
turboprop multiengine airplanes. The FAA ultimately accepted thirty-
nine of the forty-one ARC recommendations and developed this proposed 
rulemaking in accordance with them. The two recommendations we 
disagreed with would have lowered the standards previously applied 
through special conditions.

C. Proposed Regulatory Requirements Overview

    The FAA currently issues type certificates (TCs) to part 23 
turbojets using extensive special conditions, exemptions, and 
equivalent levels of safety (ELOS). Until recently, this practice of 
using special conditions, exemptions, and ELOS did not represent a 
significant workload because there were relatively few part 23 turbojet 
programs. However, in the past five years, the number of new part 23 
turbojet type certification programs has increased more than 100 
percent over the program numbers of the past three decades. The need to 
incorporate special conditions, exemptions, and ELOS into part 23 stems 
from this rise in the number of new turbojet programs and the expected 
growth in the number of future programs. Codifying special conditions 
would standardize and clarify the requirements for manufacturers during 
the design phase of turbojets. Doing so would prevent instances where 
manufacturers design turbojets and later have to demonstrate compliance 
with special conditions that may require redesign. Codifying special 
conditions, exemptions, and ELOS would also eliminate the 
manufacturers' and the FAA's workload associated with processing these 
documents and could reduce potential delays to project schedules. Many 
of the proposed changes in this notice would codify certification 
requirements and practices currently accomplished through use of 
special conditions, exemptions, and ELOS.
    We propose changes to part 1 definitions to clarify new 
requirements proposed for part 23. In addition, we propose changes to 
part 23 in the areas of:
     Airplane categories to allow commuter category 
certification of multiengine turbojets;
     Flight requirements, including standards for performance, 
stability, stalls, and other flight characteristics;
     Structure requirements, including standards for emergency 
landing conditions and fatigue evaluation;
     Design and construction requirements, including standards 
for flutter, takeoff warning system, brakes, personnel and cargo 
accommodations, pressurization, and fire protection;
     Powerplant requirements, including standards for engines, 
powerplant controls and accessories, and powerplant fire protection;
     Equipment requirements, including general equipment 
standards and standards for instruments installation, electrical 
systems and equipment, and oxygen systems; and
     Operating limitations and information, including standards 
for airspeed limitations, kinds of operation, markings and placards, 
and airplane flight manual and approved manual material.

II. Discussion of the Proposed Regulatory Amendments

1. Part 1: Definitions Clarifying Power and Engine Terms

    We propose to amend part 1 definitions for ``rated takeoff power,'' 
``rated takeoff thrust,'' ``turbine engine,'' ``turbojet engine,'' and 
``turboprop engine.'' Defining engine-specific terms would clarify the 
new requirements proposed for part 23. The need to define some of these 
terms was also shown by the following communications between the FAA 
and members of industry. These communications were based on the 
existing part 1 definitions for ``rated takeoff power'' and ``rated 
takeoff thrust'', which limit the use of these

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power and thrust ratings to no more than five minutes for takeoff 
operation.
    In 1990, the Airline Transport Association (ATA) sent a letter to 
the FAA asking the FAA to allow 10-minute OEI takeoff approval. At some 
airports (mostly foreign), the climb gradient capability needed to 
clear distant obstacles after takeoff requires more time at takeoff 
thrust than 5 minutes. Using only 5 minutes of takeoff thrust to clear 
distant obstacles limits the maximum allowable airplane takeoff weight. 
The availability of takeoff thrust or power for use up to 10 minutes, 
granted by some foreign authorities, enabled some foreign operators to 
dispatch at an increased gross weight over that allowed for U.S. 
operators. U.S. operators asked for equal treatment in similar 
circumstances. The FAA has approved these requests when they have been 
properly substantiated. This policy would also apply to operators of 
part 23 turbojet-powered airplanes in order to achieve a climb gradient 
necessary to clear obstacles.

2. Expanding Commuter Category to Include Turbojets

    Currently, we limit commuter category airplane requirements to 
propeller-driven, multiengine airplanes. The FAA has issued exemptions 
to allow turbojets weighing more than 12,500 pounds to be certificated 
under part 23. The proposal to change Sec.  23.3 would codify the 
current FAA practice of certificating multiengine turbojets weighing up 
to and including 19,000 pounds under part 23 in the commuter category.

3. Performance, Flight Characteristics, and Other Design Considerations

a. Performance
    We propose to extend the commuter category performance requirements 
to multiengine turbojets weighing more than 6,000 pounds. This proposal 
codifies requirements that we currently impose by special conditions 
for these airplanes. Amendment 23-45 (58 FR 42136) requires all 
turbine-powered airplanes weighing 6,000 pounds or less to meet many of 
the same performance standards for reciprocating-powered airplanes 
weighing more than 6,000 pounds. The FAA has determined that turbojets 
should meet a higher level of safety than reciprocating-powered 
airplanes in the same weight band. By requiring turbojets over 6,000 
pounds to meet the higher commuter category certification requirements, 
the FAA would remain consistent in establishing more stringent 
requirements for turbojet airplanes than for reciprocating airplanes.
    The ARC recommended no changes to performance requirements in 
Sec. Sec.  23.51, 23.53, 23.55, 23.57, 23.59 and 23.61. The ARC pointed 
out that applying the commuter category takeoff performance 
requirements to multiengine turbojets weighing more than 6,000 pounds 
would include restrictions that could become a takeoff weight 
limitation for operations. The ARC stated that these requirements are 
too restrictive for part 91 operations. However, existing multiengine 
turbojets weighing more than 6,000 pounds are required to meet these 
standards through special conditions, and we have seen negligible 
operational impact. We have no rationale or basis to support a reduced 
level of safety for part 23 turbojets.
    The ARC also reviewed FAA and Flight Safety Foundation accident 
studies for engine failure on takeoff. The ARC determined that existing 
normal category part 23 turboprops operated under part 135 have an 
acceptable safety record when compared to turbojets. Furthermore, 
turboprops in the accident studies were not certificated with any of 
the commuter category performance requirements for climb gradients.
    The ARC believed the safety record of the turboprops had more to do 
with the inherent reliability of turbine engines rather than the higher 
climb gradient. An ARC member suggested the higher OEI climb gradients 
originated in part 25 during the large piston transport airplane engine 
era. Back then, the large piston engines were prone to failure on 
takeoff or initial climb, and the requirements for OEI climb gradients 
were necessary for safety.
    The ARC further believed raising the OEI climb performance 
requirements for most multiengine airplanes was appropriate. However, 
the ARC debated the appropriate OEI climb gradients for turbine-powered 
airplanes over 6,000 pounds. Based on the reliability of turbine 
engines, the ARC only recommended raising the climb performance to 1 
percent. This matched the ARC's recommendation of 1 percent for 
turbojets under 6,000 pounds. The ARC's recommendation, however, would 
reduce the OEI climb performance that is currently required through 
special conditions from 2 to 1 percent for turbojet-powered airplanes 
over 6,000 pounds.
    Existing multiengine turbojets weighing more than 6,000 pounds are 
required through special conditions to meet the commuter category 
performance requirements (2 percent climb gradient) for OEI. We propose 
to maintain the 2 percent OEI climb gradient currently applied through 
special conditions for multiengine turbojets over 6,000 pounds. This 
climb gradient requirement is safe and prudent, and it is not 
reasonable to reduce the level of safety that already exists with part 
23 turbojets.
    Although special conditions have required 2 percent OEI climb 
gradient for multiengine turbojets over 6,000 pounds, there was no data 
to support whether small turbojets under 6,000 pounds could meet the 
higher 2 percent climb gradient while maintaining reasonable utility. 
If our rule changes to Sec. Sec.  23.63 and 23.67 negatively impacted 
their utility (i.e., weight-carrying ability), the rule might give the 
piston-powered, multiengine airplanes a distinct market advantage. 
Accident studies show that turbojets are generally safer than piston-
powered airplanes. Therefore, we wanted to compromise by proposing a 
requirement that would provide an adequate minimum safety standard and 
encourage production of more turbojets. One multiengine turbojet in 
this weight band has been operated as an air taxi, and the FAA expects 
this type of operation to grow. While this particular jet is capable of 
higher climb performance, we propose only to increase the OEI climb 
performance requirement to 1.2 percent because other jets in this 
weight band may not be capable of the higher 2 percent climb 
performance. Based on accident data, 1.2 percent provides an adequate 
minimum safety standard.
    Historically, piston-powered, multiengine airplanes were allowed a 
lower climb requirement because they would not have any weight-carrying 
utility if forced to meet the same requirements of the larger 
airplanes. We are continuing this philosophy in this proposal. (See 
summary in the table below.)

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             Table 1--One-Engine Inoperative Climb Requirements to 400 Feet Above Ground Level (AGL)
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                                                                                     ARC
  Multiengine type/airplane weight band               Current rule             recommendation     FAA proposal
                                                                                  (percent)         (percent)
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Pistons >6,000 lbs.......................  Measurably positive..............               1.0               1.0
Turboprops <=6,000 lbs...................  Measurably positive..............               1.0               1.0
Turboprops >6,000 lbs....................  Measurably positive..............               1.0               1.0
Turbojets <=6,000 lbs....................  Measurably positive..............               1.0               1.2
Turbojets >6,000 lbs.....................  2.0 percent imposed through                     1.0               2.0
                                            special conditions.
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    In addition to the proposed changes in takeoff and climb 
performance requirements described above, we also propose changes to 
other performance rules. Currently, part 23 reflects the traditional 
small airplane definition of landing configuration stall speed 
(VSO). However, certification personnel have interpreted 
VSO in part 23 as being the same as that in part 25. This 
interpretation has resulted in an unnecessary burden to the applicant. 
We are revising the part 23 requirement so that it is distinct from the 
part 25 requirement and to retain the original definition of the term. 
We are proposing to revise paragraphs (a) and (c) of Sec.  23.49 to 
clarify the section. We are also proposing to correct the title of this 
section in the CFR to ``Stalling speed'' instead of ``Stalling 
period.''
    VSO, by definition, is the stall speed in the maximum 
landing flap configuration and is not applicable to other flap 
configurations. (V speeds are defined in part 1. To simplify the 
understanding of the proposed rule, we are adding this information 
here.) Current Sec.  23.73 references VSO. The reference to 
VSO in this paragraph is an error and should be changed to 
reference the stall speed for a specified flap configuration 
(VS1). The reference landing approach speed 
(VREF) should be based on 1.3 times the VS1. We 
propose to amend the standards to address airplanes certificated under 
part 23 that may have more than one landing flap setting. We also 
propose to apply the commuter category requirements for VREF 
to multiengine turbojets over 6,000 pounds maximum weight. In addition, 
we propose to apply the commuter category requirements for balked 
landings in Sec.  23.77 to all multiengine turbine-powered airplanes 
over 6,000 pounds, consistent with current special conditions for 
multiengine turbojets and turbine-powered airplanes over 6,000 pounds.
b. Flight Characteristics
    The FAA proposes to define ``maximum allowable speed'' and to 
clarify the specific speed limitations, which include specific criteria 
for VFC, VLE, or VFC/MFC as 
appropriate. The proposal for Sec.  23.177 would codify special 
conditions that include specific speed limitations. Furthermore, we are 
adding a new paragraph to Sec.  23.175(b) to define the VFC/
MFC (maximum speed for stability characteristics) term in 
part 23. This definition was inadvertently omitted in the last revision 
to part 23.
    The FAA proposes to amend the combined lateral-directional dynamic 
stability damping requirements for airplanes that operate above 18,000 
feet. The existing stability damping requirements, which apply at all 
certificated altitudes, were developed when small airplanes typically 
operated under 18,000 feet and were not equipped with yaw dampers. The 
existing requirement remains appropriate for low altitude operations, 
such as for approaches, but it is not appropriate for larger airplanes 
that typically use yaw dampers and fly at altitudes well above 18,000 
feet. The FAA has issued exemptions for most turbojets certificated 
under part 23 because it is appropriate for high-altitude, high-speed 
operations. The proposed changes to Sec.  23.181 would reduce the 
stability damping requirement at 18,000 feet and above. If adopted, 
this amendment would reduce the number of exemptions processed by the 
FAA by codifying what is allowed as an acceptable means of compliance.
    The FAA proposes to amend the existing stall requirements in 
Sec. Sec.  23.201 and 23.203 to include language from the turbojet 
special conditions. We propose clarifying the requirements for wings-
level and accelerated turning stalls. We also propose changing the 
roll-off requirements for wings-level, high-altitude stalls.
    The FAA proposes additional high-speed and high-altitude 
requirements to Sec. Sec.  23.251 and 23.253 to address the new 
generation of high performance part 23 airplanes. The FAA also proposes 
to extend provisions from part 25, Sec. Sec.  25.251(d) and (e), to 
part 23. However, we would limit the requirements to airplanes that fly 
over 25,000 feet and have a Mach dive speed (MD) faster than 
Mach 0.6 (M 0.6) to be consistent with part 25 requirements. The FAA 
also proposes the use of VDF/MDF, which is 
demonstrated flight dive speed (VDF) or Mach 
(MDF) as referenced in the part 23 turbojet special 
conditions.
    Furthermore, we propose adding requirements in a new Sec.  23.255 
that would be based on Sec.  25.255 and would address potential high-
speed Mach effects for airplanes with MD greater than M 0.6. 
The FAA's approach would only apply the part 25-based requirements to 
airplanes that incorporate a trimmable horizontal stabilizer, which is 
consistent with the ARC's recommendation. The ARC's recommendation was 
based on the positive service history with the existing fleet of part 
23 and part 25 turbojets designed with conventional horizontal tails 
that use trimmable elevators. The industry manufacturers have designed 
airplanes that have experienced upset incidents involving out-of-trim 
conditions with a trimmable horizontal stabilizer. Service experience 
shows that out-of-trim conditions can occur in flight for various 
reasons, and the control and maneuvering characteristics of the 
airplane may be critical in recovering from upsets. The proposed 
language would require exploring the airplane's high-speed control and 
maneuvering characteristics.
c. Other Design Considerations
    We propose to revise language in Sec.  23.703 in the introductory 
text and paragraph (b) to add takeoff warning system requirements to 
all airplanes over 6,000 pounds and all turbojets. The definition of an 
unsafe condition, in this case, is the inability to rotate or prevent 
an immediate stall after rotation. High temporary control forces that 
can be quickly ``trimmed out'' would not necessarily be considered 
unsafe.
    We have proposed the commuter category, rejected takeoff 
requirements for all multiengine turbojets over 6,000 pounds. The 
higher takeoff speeds and distances for these airplanes make the 
ability to stop in a specified distance a safety issue. Additional 
braking considerations accompany the rejected

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takeoff requirements. Therefore, we propose to apply the requirements 
for brakes in Sec.  23.735 to all multiengine turbojets over 6,000 
pounds, as well as to all commuter category airplanes.

4. Structural Considerations for Crashworthiness and High-Altitude 
Operations

    The FAA proposes to codify into Sec.  23.561 the recent turbojet 
special conditions that were not available during the ARC's effort. 
This proposal applies to single-engine turbojets with centerline 
engines embedded in the fuselage. Part 23 did not encompass embedded 
centerline engine installations, except for in-line propeller-pusher 
types. In light of several new turbojet designs, it is prudent to 
require greater engine retention strength for engines mounted aft of 
the cabin. This is especially true for engines mounted inside the 
fuselage behind the passengers. The proposed requirement would reduce 
the potential for the engine to separate from its mounts under forward-
acting crash loads and subsequently intrude into the cabin. We recently 
applied this proposed requirement to a single-engine turbojet through 
special conditions.
    The ARC did not consider emergency landing dynamic conditions in 
Sec.  23.562. We recognize, however, that Sec.  23.562 should be 
applicable to all turbojets, including those operating in the commuter 
category. All manufacturers of recently certificated commuter category 
turbojets have agreed to comply with Sec.  23.562. The FAA proposes to 
amend Sec.  23.562 to include all commuter category turbojets. This 
proposal would adopt current industry practice and ensure a consistent 
level of safety for all turbojets.
    At one time, the FAA proposed to apply the requirements for 
emergency landing dynamic conditions to all commuter category 
airplanes.\2\ Subsequently, we published new certification and 
operations requirements for commuter operations.\3\ These actions 
required certain commuter operators that previously conducted 
operations under part 135 to conduct those operations under part 121. 
This rule, in effect, eliminated the use of new part 23 airplanes with 
10 seats or more in scheduled service. This action negated any 
projected benefits supporting the addition of emergency landing dynamic 
conditions to commuter category airplanes.
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    \2\ 58 FR 38028.
    \3\ 60 FR 65832 and 61 FR 2608.
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    The commuter operators affected were those conducting scheduled 
passenger-carrying operations in airplanes that have passenger-seating 
configurations of 10 to 30 seats (excluding any crewmember seat) and 
those conducting scheduled passenger-carrying operations in turbojet 
airplanes regardless of seating configuration. The action increased 
safety in scheduled passenger-carrying operations and clarified, 
updated, and consolidated the certification and operations requirements 
for persons who transport passengers or property by air for 
compensation or hire.
    In terms of overall configuration, commuter category turbojets have 
little resemblance to their propeller-driven counterparts. During an 
emergency landing, most commuter category turbojets will have more 
structure underneath the cabin floor available to absorb energy than 
traditional propeller-driven airplanes. This capability, along with the 
differences in the overall airplane configuration of turbojets, would 
suggest the test conditions specified in the current rule should be 
applicable to all turbojets. However, commuter category airplanes 
cannot exceed a maximum takeoff weight of 19,000 pounds. With this 
limitation, the amount of crushable, energy absorbing structure is 
small when compared to most part 25 airplanes. For this reason, we 
propose to require the dynamic test conditions specified in part 23 
rather than those in Sec.  25.562.
    We also propose to modify the seating head injury criteria (HIC) 
calculation in the proposed rule to be consistent with the HIC 
definition in part 25. This proposal addresses the concern that the HIC 
definition in part 23 would lead to a HIC calculation only for the 
total time of the head impact, which would not necessarily maximize 
HIC.
    In the event of a ditching, the proposed change in Sec.  23.807 
would provide an alternative to meeting the current requirement for an 
emergency exit, above the waterline, on both sides of the cabin for 
multiengine airplanes. Proposed section 23.807 would allow the 
placement of a water barrier in the doorway before the door would be 
opened as a means to comply with the above waterline exit requirement. 
This barrier would be used to slow the inflow of water. The FAA has 
approved the use of this barrier as an alternative to the above 
waterline exit for several airplanes by issuing an ELOS finding.
    Several new part 23 turbojet programs include approval for 
operations at altitudes above 40,000 feet. Additionally, the FAA has 
issued special conditions for operations up to 49,000 feet. We propose 
rule changes for structures and the cabin environment to ensure 
structural integrity of the airplane at higher altitudes. We also 
propose rule changes to prevent exposure of the occupants to cabin 
pressure altitudes that could cause them physiological injury or 
prevent the flight crew from safely flying and landing the airplane.
    We propose to amend Sec.  23.831 to add new paragraphs (c) and (d), 
which include standards appropriate for airplanes operating at high 
altitudes beyond those included in part 23. The proposed changes are 
intended to ensure flight deck and cabin environments do not result in 
the crew's mental errors or physical exhaustion that would prevent the 
crew from successfully completing assigned tasks for continued safe 
flight and landing. An applicant may demonstrate compliance with 
paragraph (d) of this requirement if the applicant can show that the 
flight deck crew's performance is not degraded.
    The cabin environment must be conservatively specified such that no 
occupant would incur any permanent physiological harm after 
depressurization. The environmental and physiological performance 
limits used for demonstrating compliance must originate from recognized 
and cognizant authorities as accepted by the regulatory authority 
reviewing the compliance finding.
    As part of the certification process, we would consider the entire 
flight profile of the airplane during the depressurization event. The 
profile would include cruise and transient conditions during descent, 
approach, landing, and rollout to a stop on the runway. We would not 
include taxiing as a compliance consideration because the airplane 
would be on the ground and could be evacuated, or flight deck windows 
and cabin doors could be opened for ventilation. The condition of the 
airplane from the beginning of the event to the end of the landing roll 
is accounted for when assessing the safe exit of an airplane.
    We chose the words ``* * * shall not adversely affect crew 
performance * * *'' to mean the crew can be expected to reliably 
perform either their published or trained duties, or both, to complete 
a safe flight and landing. We have measured this in the past by a 
person's ability to track and perform tasks. The event should not 
result in expecting the crew to perform tasks beyond the procedures 
defined by the manufacturer or required by existing regulations. We use 
the phrase ``No occupant shall sustain permanent physiological harm'' 
to mean the occupants who may have required some

[[Page 41527]]

form of assistance, once treated, must be expected to return to their 
normal activities.
    To show compliance to the proposed rule, the applicant should 
consider what would happen to the airplane and systems during 
depressurization. The applicant may also consider operational 
provisions, which provide for or mitigate the resulting environmental 
effects to airplane occupants. If the manufacturer provides an approved 
procedure(s) for depressurization, the flight deck and cabin crew may 
configure the airplane to moderate either temperature or humidity 
extremes, or both, on the flight deck and in the cabin. This 
configuration may include turning off non-critical electrical equipment 
and opening the flight deck door, or opening the flight deck window(s).
    As with Sec.  23.831, we find it necessary to amend the standards 
in Sec.  23.841 to prevent exposure of the occupants to cabin pressure 
altitudes that could keep the flight crew from safely flying and 
landing the airplane or cause permanent physiological injury to the 
occupants. The intent of the proposed changes to Sec.  23.841 is to 
provide airworthiness standards that allow subsonic, pressurized 
turbojets to operate at their maximum achievable altitudes--the highest 
altitude an applicant can choose to demonstrate the effects to several 
occupant related items after decompression. The applicant must show 
that: (1) The flight crew would remain alert and be able to fly the 
airplane, (2) the cabin occupants would be protected from the effects 
of hypoxia (i.e., deprivation of adequate oxygen supply), and (3) if 
some occupants do not receive supplemental oxygen, they would be 
protected against permanent physiological harm.
    Existing rules require the cabin pressure control system maintain 
the cabin at an altitude of not more than 15,000 feet if any probable 
failure or malfunction in the pressurization system occurs. Cabin 
pressure control systems on part 23 airplanes frequently exhibit a 
slight overshoot above 15,000 feet cabin altitude before stabilizing 
below 15,000 feet. Existing technology for cabin pressure control 
systems on part 23 airplanes cannot prevent this momentary overshoot, 
which prevents strict compliance with the rule. We have granted ELOS 
findings for this characteristic because physiological data shows the 
brief duration of the overshoot would have no significant effect on an 
airplane's occupants.
    Special conditions issued for part 23 turbojets are similar and, 
for operating altitudes above 41,000 feet, equivalent to the 
requirements in Sec.  25.841 adopted in Amendment 25-87 (61 FR 28684). 
That amendment revised Sec.  25.841(a) to include requirements for 
pressurized cabins that were previously covered only in special 
conditions. The special conditions required consideration of specific 
failures. The FAA incorporated reliability, probability, and damage 
tolerance concepts addressing other failures and methods of analysis 
into part 25 after the issuance of the special conditions. Sections 
23.571, 23.573, and 23.574 address damage tolerance requirements. We 
propose to require the use of these additional methods of analysis as 
part of this rulemaking.
    This proposal also specifies a more performance-based criterion, 
such that failures cannot adversely affect crew performance nor result 
in permanent physiological harm to passengers.

    (Note: There is a different standard for the crew than the 
passengers.)

    Part 23 requires a warning of an excessive cabin altitude at 10,000 
feet. Those regulations do not adequately address airfield operation 
above 10,000 feet. Rather than disable the cabin altitude warning to 
prevent nuisance warnings, we have issued ELOS findings that allow the 
warning altitude setting to be shifted above the maximum approved field 
elevation, not to exceed 15,000 feet. We propose to revise Sec.  23.841 
to incorporate language from existing ELOSs into the regulation.
    Currently, we address oxygen systems for airplanes operating above 
41,000 feet using special conditions derived from part 25. A large 
number of new turbojets and high-performance airplanes entering part 23 
certification will operate at higher altitudes than previously 
envisioned for part 23 airplanes. We are proposing revisions to 
Sec. Sec.  23.1443, 23.1445, and 23.1447 to establish requirements for 
oxygen systems. These new requirements would eliminate the need for 
special conditions for airplanes operating above 40,000 feet.

5. General Fire Protection and Flammability Standards for Insulation 
Materials

    When we initially introduced powerplant fire protection provisions 
in part 23, we did not foresee turbojet engines embedded in the 
fuselage, nor in pylons on the aft fuselage, for airplanes certificated 
to part 23 standards. We propose to add fire protection requirements 
for turbojets in Sec. Sec.  23.1193, 23.1195, 23.1197, 23.1199, and 
23.1201. Part 23 has historically addressed fire protection through 
prevention, identification, and containment. Manufacturers have 
provided prevention through minimizing the potential for ignition of 
flammable fluids and vapors. Also historically, pilots had been able to 
see the engines and identify the fire or use the incorporated fire 
detection systems, or both. The ability to see the engine provided for 
the rapid detection of a fire, which led to a fire being rapidly 
extinguished. However, engine(s) embedded in the fuselage or in pylons 
on the aft fuselage do not allow the pilot to see a fire.
    Isolating designated fire zones, through flammable fluid shutoff 
valves and firewalls, provides for containment of a fire. Containing 
fires ensures that components of the engine control system function 
effectively to permit a safe shutdown of the engine. We have only 
required a demonstration of containment for 15 minutes. If a fire 
occurs in a traditional part 23 airplane, the corrective action is to 
land as soon as possible. For a small, simple airplane originally 
envisioned by part 23, it is possible to descend the airplane to a 
suitable landing site within 15 minutes. If the isolation means do not 
extinguish the fire, the occupants can safely exit the airplane before 
the fire breaches the firewall.
    Simple and traditional airplanes normally have the engine located 
away from critical flight control systems and the primary structure. 
This location has ensured that throughout the fire event, the pilot can 
continue safe flight and control of the airplane and predict the 
effects of a fire. Other design features of simple and traditional 
airplanes (e.g., low stall speeds and short landing distances) ensure 
that even if an off-field landing occurs, the potential for a 
catastrophic outcome is minimized.
    Specifically for airplanes equipped with embedded engines, the 
consequences of a fire in an engine embedded in the fuselage are more 
varied, adverse, and difficult to predict than the engine fire for a 
typical part 23 airplane. Engine(s) embedded in the fuselage offer 
minimal opportunity to actually see a fire. The ability to extinguish 
an engine fire becomes extremely critical due to this location. With 
the engine(s) embedded in the fuselage, an engine fire could affect 
both the airplane's fuselage and the empennage structure, which 
includes the pitch and yaw controls. A sustained fire could result in 
damage to this primary structure and loss of airplane control before a 
pilot could make an emergency landing. For embedded engine 
installations, we also propose requiring a two-shot fire-extinguishing 
system because the metallic components

[[Page 41528]]

in the fire zone can become hot enough to reignite flammable fumes 
after someone extinguishes the first fire.
    We propose to upgrade flammability standards for thermal and 
acoustic insulation materials used in part 23 airplanes. The current 
standards do not realistically address situations where thermal or 
acoustic insulation materials may contribute to propagating a fire. The 
changes we propose are based on the requirements in Sec.  25.856(a), 
which were adopted following accidents involving part 25 airplanes, 
such as the Swissair MD-11. We believe the proposed standards would 
enhance safety by reducing the incidence and severity of cabin fires, 
particularly those in inaccessible areas where thermal and acoustic 
insulation materials are installed.
    The proposed standards include new flammability tests and criteria 
that address flame propagation, which would apply to thermal/acoustic 
insulation material installed in the fuselage of part 23 airplanes. 
Certification tests would consist of samples of thermal/acoustic 
insulation that would be exposed to a radiant heat source and a propane 
burner flame for 15 seconds. The insulation must not propagate flame 
more than 2 inches away from the burner. The flame time after removal 
of the burner must not exceed 3 seconds on any specimen. (See proposed 
Part II, Appendix F to part 23 for more details.)
    Current flammability requirements focus almost exclusively on 
materials located in occupied compartments (Sec.  23.853) and cargo 
compartments (Sec.  23.855). The potential for an in-flight fire is not 
limited to those specific compartments. Thermal/acoustic insulation can 
be installed throughout the fuselage in other areas, such as 
electrical/electronic compartments or surrounding air ducts, where the 
potential also exists for materials to spread fire. Proposed Sec.  
23.856 accounts for insulation installed within a specific compartment 
in areas the regulations might not otherwise cover. Proposed Sec.  
23.856 would be applicable to all part 23 airplanes, regardless of size 
or passenger capacity. Advisory material describing test sample 
configurations to address design details (e.g., tapes and hook-and-loop 
fasteners) is available in DOT/FAA/AR-00/12, Aircraft Materials Fire 
Test Handbook, dated April 2000. A copy of the handbook has been placed 
in the docket for this rulemaking.
    Insulation is usually constructed in what is commonly referred to 
as a ``blanket.'' Insulation blankets typically consist of two things: 
(1) A batting of a material generically referred to as fiberglass 
(i.e., glass fiber or glass wool), and (2) a film covering to contain 
the batting and to resist moisture penetration, usually metalized or 
non-metalized polyethylene terephthalate (PET), or metalized polyvinyl 
fluoride (PVF). Polyimide, a heat-resistant fiber used in insulation 
and adhesive, is another film used on certain airplanes. Regardless of 
the film type used, there are variations associated with its assembly 
for manufacture that result in performance differences from a fire 
safety standpoint. These variations include the density of the film, 
the type and fineness of the scrim bonded to the film, and the adhesive 
used to bond the scrim to the film. The scrim resembles a screen, and 
the mesh can vary in fineness. The scrim is usually constructed of 
either nylon or polyester and is bonded to the backside of the film to 
add shape and strength to the surface area. The adhesive used to bond 
the scrim to the film also varies. However, the type of adhesive used 
is important because fire retardant is frequently concentrated in the 
adhesive of the assembled sheet.

6. Powerplant and Operational Considerations

    Current Sec.  23.777 standardizes the height and location of 
powerplant controls because pilots may become confused and use the 
wrong controls on propeller-driven airplanes. This requirement, 
however, does not include single-power levers (which are typical for 
electronically-controlled engines). The FAA currently makes an ELOS 
finding for each airplane program that includes a single-power lever. 
We propose to revise paragraph (d) in Sec.  23.777 to incorporate the 
ELOS language.
    We propose to revise Sec.  23.903, paragraph (b)(2), to add 
requirements for fuselage-embedded, turbofan engine installations. 
These types of engine installations may have a negative impact on 
passenger safety because passengers occupy an area directly ahead of 
the turbojet engine fan disk. Certain turbofan engine designs have 
failure conditions that allow the fan disk to exit the front of the 
engine. This failure condition occurs if engines have bearing/shaft 
configurations that would allow the disk to separate from the engine 
and travel forward. If the engine has demonstrated this failure mode or 
if an analysis shows such a failure is conceivable, then the 
requirements of this section would apply. This requirement would be 
applicable to engines embedded in the airplane's fuselage where it 
could move forward into areas occupied by passengers or crew when a 
disk fails.
    In addition to the changes described above, we also propose 
requiring that electronic engine control systems meet the equipment, 
systems, and installation standards of Sec.  23.1309. We have applied 
this requirement to all digital engine controls in part 23 airplanes by 
special condition. The proposed rule change for Sec.  23.1141 would 
largely eliminate the need to issue special conditions on future 
certification programs.
    The ARC believed few single-engine airplane manufacturers have 
analyzed the criticality of their control system to meet the 
requirements of this proposed rule. The fundamental rule change 
recommended by the ARC for Sec.  23.1141 was not intended to invalidate 
or overrule the 14 CFR part 33 certification requirements. The proposed 
change for Sec.  23.1141 is intended for consideration of the airframe/
engine interface and how that interface protects against high intensity 
radiated fields (HIRF) and lightning.
    Over the years, airplane engines, including turbines, generated 
their own ignition system electrical power separate from the airplane's 
electrical generation system. Even with a complete electrical failure 
of the primary electrical systems, the engines would still run and be 
fully functional. However, all new engines are not designed with self-
electrical-generation capability. Some new engines rely on the 
airplane's electrical system to continue running and to be fully 
functional. Revising Sec.  23.1165(f) would ensure that when approved 
engines are installed on part 23 airframes, the engine ignition system 
is identified as an essential load. This would ensure that those 
engines have power during emergencies.\4\
---------------------------------------------------------------------------

    \4\ Under the proposed changes, we would certificate new 
engines, which include electronic ignition systems and engines with 
electronic controls necessary for the engine's operation, through 
the Engine and Propeller Directorate.
---------------------------------------------------------------------------

7. Avionics, Systems, and Equipment Changes

    Updated system requirements should reduce the regulatory burden on 
the applicant by clarifying and expanding the applicability of 
Sec. Sec.  23.1301 and 23.1309 to specific systems and functions. Most 
new part 23 airplane manufacturers are installing electronic primary 
flight displays (PFD) and multifunction displays (MFD) that replace 
conventional electromechanical and mechanical instruments. These new 
systems also offer more capability, reliability, and features that 
improve safety.

[[Page 41529]]

    We propose changes that would address displays, software, hardware, 
and power requirements. Besides advanced avionics and integrated 
systems, we propose to update the certification requirements to 
consider other advanced technologies (e.g., digital engine controls). 
We intend to apply lessons learned from recent small turbojet 
certification programs to update requirements for intended function and 
system safety.
    The ARC did not make a specific recommendation for Sec.  23.1301. 
However, the FAA seeks to clarify the intent of this section because it 
is frequently misinterpreted and misapplied. Clarifying the intent of 
Sec.  23.1301 would improve standardization for systems and equipment 
certification, particularly for non-required equipment and non-
essential functions embedded within complex avionic systems. Our intent 
is for the applicant to define proper functionality and to propose a 
means of compliance acceptable to the Administrator. We expect 
applicants to coordinate or negotiate deviations from established means 
of compliance with the Administrator as early as possible to minimize 
delay to project schedules.
    We propose to remove Sec.  23.1301(d), which currently states that 
equipment must ``function properly when installed.'' The proposed 
change would limit the scope of the rule since it would apply only to 
equipment required for type certification or operation. We propose a 
related change to clarify similar language in Sec.  23.1309 for proper 
functionality of installed equipment.
    The ARC did not make a specific recommendation for Sec.  23.1303. 
However, the FAA seeks to clarify the intent of this rule to 
accommodate new technology and eliminate the need to issue an ELOS for 
part 23 airplanes. We propose to amend Sec.  23.1303(c) by changing the 
current requirement from ``A direction indicator (non-stabilized 
magnetic compass)'' to ``A magnetic direction indicator.'' Section 
23.1303 does not include a direction indicator, other than the typical 
non-stabilized compass for part 23 airplanes. As new technology becomes 
more affordable for part 23 airplanes, many electronic flight 
instrument systems will use magnetically stabilized direction 
indicators (or electric compass systems) to measure and indicate the 
airplane heading to provide better performance.
    Current regulations require powerplant displays, referred to as 
``indicators'' in Sec.  23.1305, to provide trend or rate-of-change 
information. Advisory Circular (AC) 23.1311-1B, Installation of 
Electronic Displays in Part 23 Airplanes, dated June 14, 2005, 
currently provides a basis for an ELOS finding for digital engine 
display parameters.\5\ The proposed rule changes to Sec. Sec.  23.1303, 
23.1305, and 23.1311 would largely eliminate the need to issue ELOS 
findings for these systems and help standardize certification of new 
technology.
---------------------------------------------------------------------------

    \5\ A copy of the advisory circular is available on the Internet 
at https://www.faa.gov/regulations_policies/.
---------------------------------------------------------------------------

    The ARC also did not make a specific recommendation for Sec.  
23.1307. However, the FAA seeks to clarify language so applicants 
understand they may need additional equipment to operate their 
airplane. Part 23 is a minimum performance standard, and it may not 
include all the required equipment for commercial operations under 14 
CFR part 135. We propose to include parts 91 and 135 operations as 
examples to use when deciding which equipment is necessary for an 
airplane to operate at the maximum altitude.
a. System SafetyAssessment Requirements
    We originally designed the system safety assessment requirements of 
Sec.  23.1309 to address certification of electronic systems driven by 
microprocessors and other complex systems. However, the requirements of 
Sec.  23.1309 are being applied to conventional mechanical and 
electromechanical systems with well-established design and 
certification processes. This was not our intent, and we propose to 
revise Sec.  23.1309 to clarify the intended application of the rule.
    Proposed changes for Sec.  23.1309 also clarify the intent for 
certification of electronic engine controls. The current section 
excludes systems certificated with the engine. Therefore, we use 
special conditions for all electronic engine control installation 
approvals to capture the evaluation requirements of Sec.  23.1309. We 
applied special conditions to the interface of the electronic engine 
control system and the airplane. We also applied special conditions to 
verify that the installation does not invalidate the assumptions made 
during part 33 certification of the engine. This proposal would address 
electronic engine controls and eliminate the need for special 
conditions to apply Sec.  23.1309 to electronic engine control systems.
    Proposed Sec.  23.1309(a) would have requirements for two different 
types of equipment and systems installed in the airplane. Proposed 
Sec.  23.1309(a)(1) would cover the equipment and systems that have no 
negative safety effect and those installed to meet a regulatory 
requirement. Such systems and equipment are required to ``perform as 
intended under the airplane operating and environmental conditions.'' 
Proposed Sec.  23.1309(a)(2) would require the applicant to show that 
all equipment and systems (including approved ``amenities,'' such as a 
coffee pot and entertainment systems) have no safety effect on the 
operation of the airplane. The phrase ``improper functioning'' 
identifies equipment and system failures that have a potentially 
negative effect on airplane safety. Therefore, we must consider their 
potential failure condition(s). Using Sec.  23.1309, we must analyze 
any installed equipment or system that has potential failure 
condition(s) that are catastrophic, hazardous, major, or minor to 
determine their impact on the safe operation of the airplane.
    We propose to clarify the certification requirements, environmental 
qualification test requirements, and our intent for determining proper 
``intended function'' of non-required systems and equipment that do not 
have a safety effect on the airplane. A problem with the current 
requirements for airplane manufacturers arises when certification 
authorities question installation of non-required systems and equipment 
that do not perform following their specifications and, therefore, are 
``not functioning properly when installed.'' Usually, normal 
installation practices can be based on a relatively simple qualitative 
installation evaluation. If the possible safety impacts (including 
failure modes or effects) are questionable, or isolation between 
systems is provided by complex means, more formal structured evaluation 
methods or a design change may be necessary. We do not require these 
types of equipment and systems to function properly when installed. 
However, we would require them to function when they are tested to 
verify that they do not interfere with the operation of other airplane 
equipment and systems and do not pose a hazard in and of themselves.
    Also under proposed changes to Sec.  23.1309(a), we would replace 
the conditional qualifiers of ``under any foreseeable operating 
condition,'' contained in the current Sec.  23.1309(b)(1), with ``under 
the airplane operating and environmental conditions.'' Our intent with 
this proposal is for the applicant to take two actions. First, the 
applicant must consider the full normal operating envelope of the 
airplane, as defined by the airplane flight manual (AFM), with any 
modification to that envelope associated with abnormal or emergency 
procedures and any anticipated crew

[[Page 41530]]

action. Second, the applicant must consider the anticipated external 
and internal airplane environmental conditions, as well as any 
additional conditions where equipment and systems are assumed to 
``perform as intended.'' We propose to make this change in response to 
an observation that although certain operating conditions are 
foreseeable, achieving normal performance when they exist is not always 
possible (e.g., you may foresee ash clouds from volcanic eruptions, but 
airplanes with current technology cannot safely fly in such clouds).
    The FAA currently accepts equipment that is susceptible to failures 
if these failures do not contribute significantly to the existing risks 
(e.g., some degradation in functionality and capability is routinely 
allowed during some environmental qualifications, such as HIRF and 
lightning testing). System lightning protection specifically allows the 
loss of function and capability of some electrical/electronic systems 
when the airplane is exposed to lightning, if ``these functions can be 
recovered in a timely manner.''
    Proposed Sec.  23.1309(a)(3) is applicable for all functional 
reliability, flight testing, or flight evaluations. This proposed 
change clarifies the FAA's expectations for functional testing during 
certification of complex systems, but it is not meant to increase the 
testing burden on the applicant. The FAA's intent is to prohibit 
certification of systems with known defects in required functions that 
could impact safety. For example, it would not be acceptable for an 
integrated avionics system to be approved until known functional 
defects in required functions are corrected. The system would not be 
allowed to exhibit unintended or improper functionality for flight 
critical functions. The rate of occurrence of failures, malfunctions, 
and design errors must be appropriate for the failure condition(s) of 
the type of system and airplane.
    Proposed Sec.  23.1309(b) would codify a long-established means of 
compliance with current Sec.  23.1309(b) and update failure 
condition(s) terminology used in related system safety assessment 
documents developed by industry working groups (e.g., RTCA and the 
Society of Automotive Engineers (SAE)). This means of compliance 
identifies four classes of airplanes as defined in Appendix K of this 
proposal and applies appropriate probability values and development 
assurance levels for each class. The original text of Sec.  
23.1309(b)(4) has been retained and appears as Sec.  23.1309(b)(5) in 
this revision. The proposed changes to Sec.  23.1309(c) and (d) are 
meant to define the proper scope and intent for applying Sec.  23.1309 
depth of analysis for system safety assessments to all systems.
    With proposed Sec.  23.1309(f), we would make Sec.  23.1309 
compatible with the current Sec.  23.1322 (``Warning, caution, and 
advisory lights'') that distinguishes between caution, warning, and 
advisory lights installed on the flight deck. Rather than only 
providing a warning to the flight crew, which is required by the 
current rule, proposed Sec.  23.1309(f) would require that information 
concerning an unsafe system operating condition(s) be provided to the 
flight crew.
    A warning indication would still be required if immediate action by 
a flight crewmember were required. The particular method of indication 
would depend on the urgency and need for flight crew awareness or 
action that is necessary for the particular failure. Inherent airplane 
characteristics may be used in lieu of dedicated indications and 
annunciations that can be shown to be timely and effective. The use of 
periodic maintenance or flight crew checks to detect significant latent 
failures when they occur should not be used in lieu of practical and 
reliable failure monitoring and indications.
    Proposed Sec.  23.1309(f) would clarify the current rule by 
specifying that the design of systems and controls, including 
indications and annunciations, must reduce crew errors that could 
create more hazards. The additional hazards to be minimized would be 
those that are caused by inappropriate actions made by a crewmember in 
response to the failure, or those that could oc